Navigation systems for tracking the position of one or more work targets located inside a body, either alone or in relation to one or more various working tools, are used in many types of applications. One application in which navigation systems are commonly used is in the field of navigated surgical procedures. In this field, surgical navigation systems are now commonly used to assist in planning a surgical procedure or executing a planned surgical procedure, so as to improve the accuracy of the surgical procedure and minimize the invasiveness thereof.
In some surgical navigation systems, a rigid trackable device is secured to the patient so as to be fixed in relation to some portion of the patient's body. A computer implemented tracking system is used to track the position of the trackable device and, based on a previously determined spatial relationship between the trackable device and some area of interest within the patient, thereby track the position of a work target within the patient. The computer-implemented tracking system is also used to track the position of a surgical working tool, for example by means of a second trackable device secured to the working tool. From these two tracked positions, the navigation system thereby is able to track the position of the working tool relative to the working target within the patient. The tracking information is then correlated with previously defined surgical plan information relative to one or more intra- or pre-operative scan information data sets, such as CT (computer tomography) images, MRI (magnetic resonance imaging) images, X-ray images, ultrasound image data, or other similar information about the body of the patient, by one or more methods of registering the pre-operative scan information data to the intra-operative tracking information.
A limiting design parameter of such a navigation system is that the trackable device usually must be invasively attached to the patient, such as with pins or other fasteners securely fastened to a bone. Such securement can lead to additional possibilities for potential problems with post-surgical recovery of the patient. Additionally, the various navigational routines implemented by the computer-implemented tracking system are based on the assumption that the trackable device does not move relative to the patient and the target area during a navigation procedure. Therefore, movement of the trackable device relative to the patient during a navigation process, such as by accidental bumping, loss of fixation, or other means, can lead to excessive errors and require a complete re-setting or reconfiguration of the navigation system, which can use up valuable time during a surgical procedure.
Other surgical navigation systems use a trackable device formed of a flexible substrate with several LEDs (Light Emitting Diodes) carried by the flexible substrate. The flexible substrate is secured to the skin of the patient in a manner and location to prevent or minimize deformation or movement relative to the features of the patient. Thus, the trackable device is generally attached to very bony areas of the patient, such as the skull and/or nose portions so as to remain in a fixed position relative to a work target inside the patient once a navigation procedure has begun. A limitation with such a navigation system, however, is that any deformation of the trackable device once a navigation procedure has been started can lead to excessive navigation errors and or require reconfiguration of the navigation system.